1. Field of Art
This disclosure relates to ultrasonic flow meters. More particularly, the disclosure relates to a transformer board that enables positioning of transformers, coupled to transducers located within an ultrasonic flow meter, outside of the pressure boundary of the flow meter.
2. Description of Related Art
After hydrocarbons have been removed from the ground, the fluid stream (such as crude or natural gas) is transported from place to place via pipelines. It is desirable to know with accuracy the amount of fluid flowing in the stream, and particular accuracy is demanded when the fluid is changing hands, or “custody transfer.” Even where custody transfer is not taking place, however, measurement accuracy is desirable.
Ultrasonic flow meters may be used in situations such as custody transfer. An ultrasonic flow meter includes two or more transducers, each contained within a housing secured inside of a port in the body, or spool piece, of the flow meter. To contain fluid within the flow meter, an end connector is secured over each transducer port. Thus, the spool piece and end connectors create a pressure boundary that contains fluid flowing through the meter. To measure fluid flow through the meter, a pair of transducers is positioned along the inner surface of the spool piece, such that each transducer faces the other. Each transducer includes a piezoelectric element, and when an alternating current is applied to the piezoelectric element of the first transducer, the piezoelectric element responds by radiating an ultrasonic wave in the fluid passing through the flow meter. When the wave is incident upon the piezoelectric of the second transducer, that transducer responds by generating an electric signal. Some time later, an alternating current is applied to the piezoelectric element of the second transducer, and the piezoelectric element responds by radiating an ultrasonic wave through the fluid in the flow meter. When the wave is incident upon the piezoelectric of the first transducer, that transducer responds by generating an electric signal. In this way, the transducers transmit and receive signals back and forth across the fluid stream.
Each transducer is coupled to a cable that extends through the end connector and along the outer surface of the spool piece to a remote location, such as an electronics base enclosure mounted to the spool piece. The cable carries the signal created by the piezoelectric element to an acquisition board positioned within the electronics base enclosure, where the signal may be processed and subsequently used to determine the fluid flow rate through the meter.
When not in use, the piezoelectric elements in the transducers can build up an electrical charge. The electric charge presents a hazard to individuals performing maintenance on the flow meter. To reduce the risk to maintenance personnel, each piezoelectric element is coupled to a transformer, which, in addition to functions discussed below, provides a discharge path for an electrical charge created by the piezoelectric element.
The transformer also provides impedance matching between the piezoelectric element of the transducer and an acquisition device that ultimately receives the signal generated by the piezoelectric element. Thus, the transducer and the transformer are matched. For this reason, the transformer in the related art is positioned within the transducer. When either the transducer or the transformer requires replacement, both components are replaced because they are matched.
Positioning the transformer within the transducer exposes the transformer to the same conditions as those experienced by the transducer. Such exposure is undesirable when the transformer limits the transducer size or is not designed for the same conditions as the transducer. For example, the fluid passing through the meter may be corrosive. While the transducer may be compatible with corrosive conditions, the transformer may not. In such circumstances, the corrosive fluid may damage the transformer and associated electrical wiring.
One way to prevent corrosion damage to the transformer may be to encase the transformer within a material that can withstand a corrosive environment. However, such a process may be prohibitively costly.